(i) Field of the Invention:
This invention relates to novel chalcone derivatives and ultraviolet absorbers comprising the derivatives.
(ii) Description of the Prior Art:
It is known that ultraviolet rays bring about various changes in the skin. From the dermatological standpoint, the ultraviolet rays are broadly classified on the basis of the wavelength into a long wavelength ultraviolet ray of 400 to 320 nm, a medium wavelength ultraviolet ray of 320 to 290 nm and a short wavelength ultraviolet ray of below 290 nm. These rays are, respectively, called UV-A, UV-B and UV-C.
Ordinarily, a typical source of UV rays to which men are exposed is sunlight. Ultraviolet rays from sunlight which can reach the ground surface are UV-A and UV-B. UV-C is absorbed with the ozone layer and does rarely reach the ground surface. Of the ultraviolet rays which reach the ground surface, UV-B acts to form erythema and blisters and brings about changes in the skin such as accelerated formation of melanine, pigmentation and the like upon irradiation on the skin in amounts of light more than a certain level. In contrast, UV-A has been hitherto considered not to cause substantial changes in the skin. However, it has been recently disclosed by electron microscopic and histochemical techniques that the skin undergoes changes even through UV-A irradiation. In particular, the energy of UV-A, different from UV-B, arrives even at the inner skin and will bring about slight chronic changes in elastic fibers of blood vessel and connective tissues. These changes are considered to lead to promoted senility of the skin. It is also known that UV-A has the action of melanizing the skin (time-limit melanization) immediately after irradiation thereof and acts to increase the degenerative action of UV-B on the skin. UV-A is thus considered to be one of factors of developing and exacerbating moth patches and freckles.
As will be apparent from the above, it is important to protect the skin not only from UV-B, but also from UV-A in the sense that the skin is prevented from promoting the senility and the development and exacerbation of moth patches and freckles are prevented.
However, the studies on the action of UV-A on the skin have only a short history and only a slight number of substances capable of effectively absorbing UV-A when applied to the skin are known at present, including dibenzoylmethane derivatives and cinnamic acid derivatives (German Patent Laid-open Nos. 2728241 and 2728243, and Japanese Laid-open Patent Application Nos. 51-61641, 52-46056, 57-59840 and 57-197209).
Therefore, there is a high demand of development of protective agents which are able to absorb harmful UV-A to effectively protect the human skin therefrom. Such protective agents should satisfy the following requirements.
(1) A maximum absorbing capacity at a wavelength in the vicinity of 350 nm.
(2) A satisfactorily high molar absorptivity coefficient at the above wavelength.
(3) A small absorptivity of visible light because coloration of cosmetic compositions are not desirable, i.e. should be nearly zero (.epsilon..apprxeq.0) over 400 nm.
(4) High stability against heat and light.
(5) No toxic, irritative and other harmful actions against the skin.
(6) Good compatibility with cosmetic substrates.
(7) Unlikelihood to be percutaneously absorbed upon application to the skin and removed such as by sweating, or effective continuance of the efficacy.